openssh: remove unnecessary $FreeBSD$ tags

Diff reduction against upstream: remove $FreeBSD$ tags from files where
the tag itself is the only difference from upstream.

(cherry picked from commit 0e642632e6)

crypto/openssh/mux.c

@@ -18,7 +18,6 @@
 /* ssh session multiplexing support */
 
 #include "includes.h"
-__RCSID("$FreeBSD$");
 
 #include <sys/types.h>
 #include <sys/stat.h>

crypto/openssh/sftp-common.c

@@ -25,7 +25,6 @@
  */
 
 #include "includes.h"
-__RCSID("$FreeBSD$");
 
 #include <sys/types.h>
 #include <sys/stat.h>